Not applicable.
(1) Field of the Invention
This invention generally relates to a towed acoustic source. More particularly, the invention relates to a towed acoustic source that consists of a volumetric array of transducers encapsulated in a solid block of material, the solid block of material particularly formed in the shape of a towed body.
(2) Description of the Prior Art
Traditionally, towed active sonar arrays are made of metal or composite structures that house transducer arrays. The transducers themselves have rubber boots surrounding them to prevent water from intruding, and the towed body itself is free-flooding. The towed body is connected to a vessel by an electro-optical-mechanical tow cable. Thus, a problem exists in the art whereby it is necessary to separately protect the transducers from seawater within the towed body in order to preserve the electrical connections.
The following patents, for example, disclose various types of towed acoustic devices, but do not disclose an array of transducers encapsulated within a solid block of material, the solid block of material forming the external shape of the towed body as does the present invention.
U.S. Pat. No. 5,781,506 to Peloquin;
U.S. Pat. No. 5,856,954 to Grall;
U.S. Pat. No. 5,909,408 to Warnan et al.;
U.S. Pat. No. 6,050,361 to Ruffa et al.; and
U.S. Pat. No. 6,088,296 to Seaman et al.
Specifically, Peloquin disclose a method and system provided for frequency filtering compressional wave energy. An elastic cylinder is filled with fluid that is selected based on a fluid density xcfx811, and a dilational wave phase velocity c1 thereof. An elastic cylinder so-filled is subjected to a compressional wave propagating in a fluid environment, a first radial resonance frequency of the elastic cylinder is controlled by the fluid density xcfx811 and the dilational wave phase velocity cl. Further tuning of the first radial resonance frequency can be achieved by adjusting the radial wall thickness of the elastic cylinder.
The patent to Grall discloses a process of acoustic emission for sonar with a separate emission array from the receiving array. The emission array has the shape of a linear acoustic array and can either be towed simultaneously with a linear acoustic receiving array or be suspended from a helicopter to form a xe2x80x9cdippingxe2x80x9d type sonar. Detection using this type of sonar is facilitated by increasing the sound level via the directivity index, while reducing the level of reverberation originating from the bed and from the surface of the sea.
Warnan et al. discloses a towed acoustic transmitter forming an underwater vehicle which is itself intended for towing a linear acoustic receiving array. It consists in placing the vertical faired acoustic array of such a transmitter at the very rear of the underwater vehicle, and in balancing the weight of this array by a faired ballast situated at the very front thereof. These two parts are joined by a girder of a small cross-section, and the center of gravity of the whole is situated at the front of this girder and beneath it. The vehicle is towed by a cable fastened to the vehicle by a hook fixed to a swivel joint above the center of gravity. This towing makes it possible to facilitate the operations of submersion and fishing-out of the whole while also achieving a greater depth of submersion.
Ruffa et al. discloses a cavitation-resistant sonar array having reduced spacing between transducer elements. The array has a series of transducer elements attached to an array fixture with spacing between elements being fixed at one-quarter wavelength or closer. Cavitation caused by this close spacing is eliminated by replacing water spaces between elements with a rho-c rubber which matches the acoustic impedence, z, of water, that is z=xcfx81c. The rho-c material is bonded to the transducer elements to prevent a loss of contact between the transducer elements and the spacer. A processing computation correcting the signal data is provided to account for any differences in the speed of sound, c, in the rho-c material when compared to the speed of sound in water.
Seaman et al. disclose a soft body, towable, active acoustic module including a specially formed suspension fixture and a flexible faired body enclosing an active acoustic array. The suspension fixture is a Y-shaped termination having a single forward end and two trailing ends, one for attachment of a trailing tow cable and towed receiver array and the other for attachment of the flexible faired body. The flexible, faired body is an elongated hydrofoil having sections which allow lateral bending. The combination of the suspension feature and lateral bending feature allows the module to be deployed and recovered through underwater shipboard deployment tubes. A weight attached to the faired body near the lower rear end balances the body to maintain a substantially vertical position during towing.
It should be understood that the present invention would in fact enhance the functionality of the above patents by providing a solid casting of a waterproof material around a plurality of active acoustic elements, and more particularly, providing the solid casting in the shape of a towed body.
Therefore it is an object of this invention to provide an encapsulated acoustic array within a towed body.
Another object of this invention is to provide a towed body having the acoustic array thereof encapsulated in a solid casting of material, such as polyurethane or any other suitable material.
Still another object of this invention is to provide a towed body having the acoustic array encapsulated in a solid casting of material, such that at least a portion of the solid casting material defines an outer surface of the towed body.
A still further object of the invention is to provide a towed body formed of a solid casting material, the solid casting material fixing an acoustic transducer array therein in a watertight manner.
Yet another object of this invention is to provide a solid casting in the shape of a towed body, the towed body housing a plurality of fixed and environmentally protected acoustic transducers therein.
In accordance with one aspect of this invention, there is provided an encapsulation assembly. The encapsulation assembly includes a housing having a nose end, a tail end, and a body portion between the nose end and the tail end. A plurality of acoustic transducers are positioned within the housing, each of the plurality of acoustic transducers having a wiring connection attached thereto. A tow cable is connected to the nose end of the towed body and is in communication with a wiring connection from each of the plurality of acoustic transducers. A characteristic of the assembly is that the solid plastic material is formed in the shape of at least the body portion of the housing thereby environmentally isolating the plurality of acoustic transducers within the housing. Embedding transducers in a solid material has been described previously by Ruffa and Stottlemyer (U.S. Pat. No. 6,050,361). However, the unique aspect of the present invention is that the acoustic elements are not only embedded in the solid material, but the material is cast in the shape of a towed body.